The first of the Scud series, designated R-11 and designated by NATO as the SS-1B Scud-A originated in a 1951 requirement for a ballistic missile with similar performance to the German V-2 rocket, but half its size. The design first flew on 18 April 1953. A production order followed on 13 December 1953 and in July 1955 the R-11 was formally accepted into military service with the Soviet armed forces. The definitive R-11M, designed to carry a nuclear warhead, was accepted officially into service on 1 April 1958. The unguided Scud-A missile remained in service with the USSR until 1973.